a. Field of the Invention
The instant invention relates to active current sharing in a multiphase DC-DC converter.
b. Background
Power supplies for high performance microprocessors often must deliver low supply voltages with high currents while maintaining tight output voltage regulation in the presence of large load transients. Interleaved multiphase converters have been used in such systems due to advantages, such as lower switching frequencies for each phase, total current division among the phases, fast transient response, and use of smaller active and passive components. Multiphase converters, however, generally require additional circuitry to ensure appropriate current sharing and phase shifting between the phases.
Many analog approaches have been used to achieve current sharing. “Master-slave” schemes, for example, include a converter that operates as a master converter to regulate the current of that converter and other slave converters via a reference signal. “Democratic” or “autonomous” schemes have also been used in which multiple converters are connected to an analog sharing line to produce a current reference and the individual converters are controlled to match their output currents to the current reference. “Central-limit” schemes utilize a central controller to provide a current error of each phase relative to the average load current. In each of these approaches, however, the master must receive information from each phase. This results in a delay in the controller while information is transferred and requires dedicated traces to each phase (resulting in a relatively large board area) and a communication protocol so that information can be through the phases or across a shared bus (e.g., a CAN bus, a daisy-chain, etc.).
Digital control approaches have also been proposed for multiphase converters in order to provide for increased design flexibility and programmability, immunity to analog component variations, ease of integration with other digital systems, and the ability to implement more advanced control schemes. Previously proposed digital control approaches, however, have been based on a master digital controller in which one of the digital controllers (or another dedicated digital controller that is not part of a phase) operates as a master controller to regulate the current of that converter and other slave via a reference signal. In each of these cases, however, a relatively large area of a PC board and number of hard wired communications configurations between the phases and/or the dedicated master and the phases.